The following invention relates to probes for use with electronic test instruments for testing circuit components such as integrated circuits and circuit elements of hybrid circuits.
Conventionally, integrated circuits and hybrid circuits are tested by placing those circuits in a chuck which is then positioned relative to a probe card which contains a plurality of probes soldered or attached to the card in predetermined positions so as to make contact with certain desired portions of the circuit under test. The probe cards are planar mounting boards having a central aperture about which the various probes are mounted. Transmission lines such as coaxial cables are attached to each of the probes and their opposite ends are then connected to a test instrument for gathering data sensed by the probes.
The probes that are mounted and used in this manner are either DC probes (probes that can measure only at very low frequencies) or are characteristically low impedance probes which are wideband probes but whose input impedance is typically on the order of 50 ohms. The DC probes are incapable of measuring high frequency phenomena and, the low impedance probes load the circuit under test and interfere with the parameter that is to be measured.
High impedance probes having the proper bandwidth are available; however, these must include active circuitry. Currently such probes comprise a housing which is intended to be hand-held and a probe tip protruding from the housing. Such probes cannot easily be usd with probe cards because of the size and configuration of the circuit elements which must be contained within the housing. To the extent that such probes can be adapted to be physically attached to probe cards, such arrangements are awkward and their size interferes with adjustments that are sometimes made to the circuit under test. These adjustments frequently take the form of laser trimming and the probe frequently masks the area where the laser should be applied.